1. Technical Field
The present invention relates to an ink composition that contains a fluorescent dye and an ink jet printing method using the ink composition.
2. Related Art
Red fluorescent inks have been used in printers for affixing a mark to metered mail. In particular, in North America, the United States Postal Service have designated red fluorescent inks that can be read with automatic reading apparatuses as inks to be used to affix a mark to metered mail.
Automatic reading apparatuses not only read bar codes, but also simultaneously identify the front side or the back side of metered mail. Red fluorescent inks. therefore must have high fluorescence intensity to reduce errors in identifying the front side or the back side of metered mail, as well as high optical density to improve the accuracy with which bar codes are read.
JP-A-9-291246 discloses a water-resistant red fluorescent ink for metered mail, which contains a glycol ether as a co-solvent penetrant.
JP-A-2006-131667 discloses a water-based fluorescent ink having excellent fluorescent color developability, which includes an aqueous fluorescent coloring dye containing C.I. Acid Red 52 and C.I. Acid Red 92 and a pigment dispersion containing C.I. Pigment Red 122.
The present inventors have found that the addition of a yellow dye C.I. Direct Yellow 87, tetraethylene glycol monoethylhexyl ether, and triethylene glycol monobutyl ether to a red fluorescent ink composition containing C.I. Acid Red 52 and C.I. Acid Red 92 can improve the fluorescence intensity and the color developability (optical density) of the red fluorescent ink composition. The invention is based on this finding.